Strings on the stack

The code

Embedded C for Cortex-M. It compiles. There are 3 real bugs in it: the kind that pass a bench test and fail in the field.

#define NAME_LEN 16

const char *fmt_temp(int16_t t_dC)
{
    char buf[16];
    snprintf(buf, sizeof buf, "%d.%d C", t_dC / 10, t_dC % 10);
    return buf;
}

void show_temp(void)
{
    lcd_print(fmt_temp(read_temp_dC()));
}

void set_zone_name(char dst[NAME_LEN], const char *src)
{
    strncpy(dst, src, NAME_LEN);
}

What an interviewer expects

• Point to each line you'd stop in a code review.
• Say what actually breaks: the failure mode, not just the rule it violates.
• Fix it, then defend the fix when asked the follow-up.

The bugs, reference fixes and the follow-up question are in the practice app, after you've tried it.

Companies that test this

Matched on the skills each company's embedded roles emphasise.

Related challenges